What are the latest developments in quantum gravity?

[wolram]

arXiv:gr-qc/0401102 v1 26 Jan 2004
A New Approach in Quantum Gravity
and its Cosmological Implications
Simone Mercuri
Giovanni Montani
ICRA—International Center for Relativistic Astrophysics
Dipartimento di Fisica (G9),
Universit`
a di Roma, “La Sapienza”,
Piazzale Aldo Moro 5, 00185 Rome, Italy.
e-mail: mercuri@icra.it, montani@icra.it PACS: 04.60.Ds – 98.80.Qc
Abstract
This work concerns a new reformulation of quantum geometrodynamics, which allows to overcome a fundamental ambiguity contained in the canonical approach to quantum gravity: the possibility of performing a (3+1)-slicing of
space-time, when the metric tensor is in a quantum regime. Our formulation provides also a procedure to solve the problems connectedto the so called frozen formalism. In particular we fix the reference frame (i.e. the lapse function and the shift vector) by introducing the so called kinematical action; as a consequence,
the new hamiltonian constraints become parabolic, so arrivingto evolutive
(Schr¨odinger-like) equations for the quantum dynamics.
The kinematical action can be interpreted as the action of a pressure less, but, in general, non geodesic perfect fluid, so in the semi classical limit our theory leads to the dynamics of the gravitational field coupled to a dust which represents the material reference frame we have introduced fixing the slicing. We also investigate thecosmological implications ofthe presence ofthe dust, which,
in the WKB limit of a cosmological problem, makes account for a dark matter component and could play, at present time, a dynamical role.

 

[marcus]

http://arxiv.org/gr-qc/0401102

"A New Approach in Quantum Gravity and its Cosmological Implications"
Simone Mercuri, Giovanni Montani
to appear on "Il Nuovo Cimento"

"This work concerns a new reformulation of quantum geometrodynamics..."

Geometrodynamics goes back to early efforts to quantize General Relativity in the 1960s and 1970s, in particular to the Wheeler-DeWitt equation.
The field lay fallow for a couple of decades.
LQG appeared and made some advances (using new variables to express the geometry)
Now interest has revived in extending the earlier approach and curing its problems (using the old, pre-LQG, variables to express the geometry)

A number of papers have come up lately like this. A notable one was
"On singularity resolution in quantum gravity"
http://arxiv.org/gr-qc/0312094
by Viqar Husain and Oliver Winkler.

It makes sense IMO for this to happen. Bojowald uses LQG and gets results like removing the BB singularity, so why shouldn't one be able to go back to Wheeler and DeWitt's old 1970s variables and get the same result? Once someone shows you can do something with LQG formalism why not go back and repeat it with the old formalism.

They seem to want to find out what went wrong in earlier attempts to quantize gravity and to find out why they got stuck back in the 1970s.

Maybe it will turn out there is nothing special about the Ashtekar new variables that LQG uses and that the old variables would have worked if they had known to do such-and-such.

Still another parallel approach that is getting people's attention is
Gambini and Pullin's discussed in their paper
http://arxiv.org/gr-qc/0402062
"Canonical quantum gravity and consistent discretizations"
Gambini gave the main survey talk on quantum gravity at a
conference in January in India.

It looks to me like the lines of quantum gravity research are
fanning out like a river delta
or perhaps it is more accurate to say that the field is running amok

It is getting too difficult to follow all the branching research lines.
but we should at least mention and notice them.

wolram your headline for this thread "A new approach to QG"
suggests to me that we should have a thread to mention and
keep track of the new and various approach(es) to quantizing general relativity.

 

[wolram]

Hi MARCUS, you say---

It is getting too difficult to follow all the branching research lines.
but we should at least mention and notice them.

wolram your headline for this thread "A new approach to QG"
suggests to me that we should have a thread to mention and
keep track of the new and various approach(es) to quantizing general relativity.
-------------------------------------------------------------------
it is difficult for me to sift out meaningful or progressive
papers, this one caught my attention because it seemed
(retro),i try to read and understand these papers before i
post them, i mostly fail but i post them in the hope that
they are of interest to others, and that some of there
learning will rub of.
it would be helpful to have a data base for these papers.